1. Field of the Invention
The present invention relates to disc brakes and clutches for vehicles generally, and more particularly to wheel brakes having wear indicating devices. The disc brake of this invention may operate in an oil bath for cooling purposes.
2. Description of the Prior Art
Wheel brakes carried on axles residing in a fluid bath are in contemporary use on vehicles such as farm machinery, as well as others. Typically, agricultural and industrial tractors are equipped with inboard brakes for the rear axle. These inboard brakes may be disc brakes which operate in an oil bath which also serves as a source of fluid for hydraulic components of the tractor as well as a lubricant for the differential. These brake systems utilize an annular piston to apply pressure to a disc which is splined to a planetary drive shaft. The opposite side of the disc adjoins a stationary outer disc ring and is in contact with it during braking. The brake operates in a fluid environment that ensures adequate cooling of the brake disc. The frictional surface on either side of the disc may have a lining of microscopically porous paper-like material bonded to either side thereof.
Through normal braking the lining is gradually worn away. When the lining is completely worn away the disc will, upon braking, be clamped between the surfaces of a brake center disc being biased by the annular piston and the pressure plate or outer disc ring. As metal-to-metal contact is now possible (as the lining material has been worn away), galling of the contacting surfaces will occur.
In brake systems without wear indicating devices the vehicle operator may not be aware that the lining has worn away. Generally when the brake lining on brakes of this type do eventually fail there will still be adequate stopping force available to control the vehicle. As a matter of fact, the vehicle operator may not be aware of brake failure until deterioration of the metal components has taken place. One of the first signs of defective brake components shows up in the hydraulic system of the vehicle as the brakes generally operate in a bath of hydraulic fluid which is also used in the vehicle hydraulic system. Hydraulic system component failures are quite possible as metal particles from the brake disc or plates may produce significant damage to filters, pumps, and piston seals.
There are brake pad wear warning systems available for use with conventional dry type disc brakes. A typical embodiment shows a metallic reed bonded to the pad backing plate perpendicular to the surface of the brake rotor. The reed contacts the rotor after the pad has partially worn away and produces an audible signal. This type of warning device could not be used for a hydraulic fluid cooled brake as it would produce metallic particles which may damage the hydraulic systems of the host vehicle.
The device disclosed herein is, to our knowledge, the only audible wear indicating device that can be effectively used with disc brakes which operate in a hydraulic fluid bath.
It is therefore, an object of this invention to present a disc brake system that has a built in warning indicator that indicates worn brakes before such wear becomes detrimental to the brake components or the various hydraulic components of the vehicle.
Another object of this invention is to present a warning device for use with liquid cooled brakes that will not detrimentally contaminate the cooling fluid.
Also an object of the invention is to present a warning system having an audible warning signal which can be heard by the vehicle operator over the noise of the vehicle.
Furthermore, it is an object of this invention to provide an audible warning device that can provide a high level of braking effectiveness.
It is also an object of the present invention to provide a warning device for use on a disc brake which is easily manufactured and relatively inexpensive.
Inasmuch as this invention could find application in other areas, such as wet or dry clutches, it is an object of this invention to provide an assembly using two frictional medias of different properties such that upon contact with a moving reactive member and a primary frictional material a first set of desirable characteristics is evident and upon contact with a secondary frictional material a second set of desirable characteristics is evident.